1. Field of Invention
The present invention relates to a resonant wireless power receiver circuit, particularly, to a resonant wireless power receiver circuit with a switching controlled rectifier circuit. The present invention also relates to a control circuit and a resonant wireless power conversion method.
2. Description of Related Art
FIG. 1 shows a prior art resonant wireless power receiver circuit 1. The resonant wireless power receiver circuit 1 comprises a resonant circuit 31, a bridge rectifier circuit 33, a DC-DC conversion circuit 34 and a load 35.
The wireless power transmission is achieved as thus. In FIG. 1, a resonant wireless power transmitter circuit (not shown) transmits a wireless power 40 to a wireless field (for example but not limited to a magnetic field, an electric field or an electromagnetic field). The wireless power 40 in the wireless field is received by the resonant wireless power receiver circuit 1 with the resonance effect of the resonant circuit 31 through for example but not limited to coupling, induced by, or capturing the wireless power 40 in the wireless field. A resonant output voltage VAC is generated at an output of the resonant circuit 31. The rectifier circuit 33 rectifies the resonant output voltage VAC to generate a rectified output voltage VRECT which is then converted by the DC-DC converter 34 to generate an output voltage VOUT to drive the load 35.
The prior art in FIG. 1 has a drawback that the rectified output voltage VRECT may be too low or too high. And, due to the uncertain level of the rectified output voltage VRECT, an extra regulation circuit (e.g. DC-DC conversion circuit 34) is required to generate a stable output voltage.
Since the operation of the prior art shown in FIG. 1 is based on resonance effect, if the resonant frequency transmitted by the resonant wireless power transmit circuit drifts from its preset frequency, or if the receiver circuit is not properly located at a proper relative distance and a proper relative angle, or if there are multiple resonant wireless power receiver circuits coupled to receive the wireless power at the same time, off resonance could happen. If the off resonance is not corrected or controlled, it could cause power loss, or the received voltage (for example the resonant output voltage VAC and the rectified output voltage VRECT) could be too low such that circuits at the following stage (such as the DC-DC converter 34 and the load 35) cannot function properly. Furthermore, nowadays there are more and more wireless power transmission applications, so in some circumstances, the resonant wireless power receiver circuit may receive wireless power transmitted from non-corresponding wireless power systems or even from other wireless communication systems (for example but not limited to NFC, Near Field Communication). Under these unexpected circumstances, the voltage (for example the resonant output voltage VAC and the rectified output voltage VRECT) received by the resonant wireless power receiver circuit 1 could be too high. An overly high voltage due to any reason could cause damage of the internal circuit or damage of the load of the resonant wireless power receiver circuit 1 (for example but not limited to the DC-DC converter 34 and the load 35).
FIG. 2 shows a Bridge Doubler Rectifier according to a prior art rectifier circuit disclosed by U.S. Pat. No. 4,268,899. When CR5 is not conductive, the Bridge Doubler Rectifier operates in 1× voltage mode, and when CR5 is conductive, it operates in 2× voltage mode. The prior art in FIG. 2 has the following drawbacks: (A) it requires two output capacitors connected to each other in series, so the equivalent capacitance is half of that of a single capacitor; (B) CR5 has to be a bi-directional control switch; (C) there are only two options for its output voltage, nevertheless as mentioned previously, since the power received by the resonant wireless power receiver circuit with resonance effect is uncertain, the output voltage generated by the prior art rectifier may be too low in 1× mode and too high in 2× mode, i.e., neither 1× nor 2× is proper, which may lead to malfunction or damage of circuits in its following stages.
FIG. 3 shows a prior art resonant wireless power receiver circuit with an over voltage protection circuit. This prior art includes a switch 220 which is connected in series between a rectifier and a target resonator. When an over voltage is detected, the switch 220 is switched OFF for over voltage protection. A drawback of this prior art is that the switch 220 must have an un-preferred relatively high voltage rating for tolerating the energy which is stored in and released from the target resonator.
Compared to the prior art in FIG. 1, the present invention has an advantage that the rectifier output is feedback controlled, such that the output voltage of the rectifier circuit is not too high nor too low. Another important advantage is that, since the present invention provides a stable rectifier output voltage or current, the DC-DC conversion circuit can be omitted, which greatly reduces the cost.
Compared to the prior art in FIG. 2, the present invention has an advantage that the rectifier output is adjustable in a continuous way, such that the output voltage of the rectifier circuit is not too high nor too low. Another advantage is that the present invention can operate with less components and with lower voltage/current rating components, so the present invention can reduce the manufacture cost.
Compared to the prior art in FIG. 3, the present invention can operate with lower voltage/current rating components, and is able to provide the over voltage/current protection using components inherent in the conventional rectifier circuit, so the present invention can reduce the manufacture cost.